Overcoat

ABSTRACT

According to embodiments, a method of forming a coating on an article includes forming a coating including an emitting layer. The emitting layer includes an elemental isotope with a known property that can be measured by a spectroscopic method. The elemental isotope provides a distinguishing identification tag for the coating, and the coating providing a layer of protection to the substrate. The method further includes depositing the coating on a surface of a substrate of the article. The elemental isotope is a stable isotope, an unstable isotope, a neutron scattering isotope, a neutron capturing isotope, or combinations thereof.

BACKGROUND

The present disclosure relates protective coatings and, moreparticularly, to protective coatings that emit, absorb, and/or scatterradiation.

Traditional manufacturing technologies and additive manufacturing (AM)technologies are widely incorporated into defense industry applications.Additive Manufacturing (AM) technologies build three-dimensional (3D)objects by adding layer-upon-layer of material(s). The material(s) canbe, for example, plastic, metal, concrete, or biological tissues. AMtechnologies use a computer, 3D modeling software (Computer Aided Design(CAD)), machinery, and layering material(s). Once a CAD sketch isproduced, the AM equipment reads data from a CAD file and disposessuccessive layers material(s), e.g., liquid, powder, or other sheetmaterial, in a layer-upon-layer fashion to fabricate a 3D object. AMtechnologies include various subsets, for example, 3D Printing, RapidPrototyping (RP), Direct Digital Manufacturing (DDM), layeredmanufacturing, and additive fabrication.

The widespread incorporation of traditional manufacturing and AMtechnologies in the defense industry means that there needs to be somemeasures to ensure that parts of the supply chain are in optimalcondition. Furthermore, the drive for extending the life of defenserelated products creates opportunities to have worn parts slipped intothe supply chain.

SUMMARY

According to embodiments, a method of forming a coating on an articleincludes forming a coating including an emitting layer. The emittinglayer includes an elemental isotope with a known property that can bemeasured by a spectroscopic method. The elemental isotope provides adistinguishing identification tag for the coating, and the coatingproviding a layer of protection to the substrate. The method furtherincludes depositing the coating on a surface of a substrate of thearticle. The elemental isotope is a stable isotope, an unstable isotope,a neutron scattering isotope, a neutron capturing isotope, orcombinations thereof.

According to other embodiments, a method of determining a need forperforming preventative maintenance on an article includes performing aspectroscopic analysis on a portion of the article including a coating.The coating includes an emitting layer. The emitting layer includes anelemental isotope that can be measured by the spectroscopic analysis,and the coating provides a layer of protection to the substrate. Themethod further includes comparing a signal received from thespectroscopic analysis to a calibration curve. The method furtherincludes determining, based on a comparison, whether the coatingprotecting the substrate has been worn and therefore whether the articleneeds maintenance. The elemental isotope is a stable isotope, anunstable isotope, a neutron scattering isotope, a neutron capturingisotope, or combinations thereof.

Yet, according to other embodiments, a coating of an article includes anemitting layer arranged on a substrate of the article. The emittinglayer includes an elemental isotope with a known property that can bemeasured by a spectroscopic method. The elemental isotope provides adistinguishing identification tag for the coating, and the coatingprovides a layer of protection to the substrate. The coating furtherincludes an attenuating layer arranged on the emitting layer. Theattenuating layer protects the emitting layer. The elemental isotope isa stable isotope, an unstable isotope, a neutron scattering isotope, aneutron capturing isotope, or combinations thereof.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts:

FIG. 1 is a cross-sectional side view of an emitting layer of a coatingarranged on a substrate according to embodiments;

FIG. 2 is a cross-sectional side view of an emitting layer of a coatingdecaying according to embodiments;

FIG. 3 is a cross-sectional side view of an emitting layer of a coatingemitting a gamma ray according to embodiments;

FIG. 4 is a cross-sectional side view of an emitting layer of a coatingaccording to embodiments;

FIG. 5 is a cross-sectional side view of a coating comprising anattenuating layer arranged on an emitting layer according toembodiments;

FIG. 6 is a cross-sectional side view illustrating wear occurring to acoating according to embodiments;

FIG. 7 is a flow chart describing a method of identifyingcharacteristics of an article using a coating according to embodiments;

FIG. 8 is a flow chart describing a method of determining a need forperforming preventative maintenance using a coating according toembodiments; and

FIG. 9 is a flow chart describing a method of passively aging a coatingaccording to embodiments.

DETAILED DESCRIPTION

As will be discussed below, embodiments disclosed herein provide methodsfor forming protective coatings on a variety of substrates. Inembodiments, methods described herein use the coatings to identify andage components safely and effectively for use domestically and abroad.In some embodiments, specific blends of isotopes, e.g., stable and/orunstable, that differ from that naturally occurring abundance ratios canbe used in the coating to identify the part lot, manufacturer, etc. Inother embodiments, gamma emitting radio-isotopes, x-ray emittingradio-isotopes, or neutron scattering isotopes are admixed asnanoparticles into a bulk overcoating material.

In embodiments, using thermal and cold spray methodologies, thenanoparticles form hard undercoat that can be protected by an optionaltop attenuating or scattering coat. Still, in other embodiments, thecoating can be a paint layer or powder coat layer, in which thenanoparticles are homogenously mixed throughout one or more overcoatlayers to serve a protective monolayer for underlying hardware. Theresulting coatings improve resistance to damage, such as corrosion andwear.

In embodiments, the coating is used to determine the need forpreventative maintenance, for example, when it is desired to service acomponent on a regular interval regardless of wear. The coatingsdescribed herein are advantageous because the amount of coating wearcorrelates with the the age of the coating. Therefore, the coating canbe passively aged to determine the amount of coating wear, and thereforeon the article. Many applicable to items have a life limit (expirationdate) regardless of wear. Identifying heavy wear on components isparticularly useful for military and defense part applications, as wellas in commercial applications.

Turning now to the Figures, FIG. 1 is a cross-sectional side view of anemitting layer 102 of a coating arranged on a surface of a substrate 101according to embodiments. The coating protects the substrate 101 of thearticle. The substrate 101 can include any bulk material. The substrate101 shown is not drawn to size, shape, or scale, and is only shown forillustrative purposes. The substrate 101 is intended to be a part orwhole of any type of article. The substrate 101 can be formed by anysuitable methods, for example, traditional manufacturing methods or AM.The substrate 101 is part of a microchip and integrated circuit inembodiments. In other embodiments, the substrate 101 can form part of anarticle (or device), such as an optical device, turbine engine fanblade, detector, or any other device, for example. While such elementsare given as examples herein, the techniques and methods disclosedherein may be used, in whole or in part, with many materials whether itis electrically active or not. The material or materials forming thesubstrate 101 are not limited to any particular type or property. Insome exemplary embodiments, the substrate 101 includes one or more of aconductive material, a semiconductor material, or an insulatingmaterial. The substrate 101 can be an article used in the defensesector, for example, wherein preventative maintenance with respect towearing and corrosion is routinely performed. The substrate 101 also canbe an article used in the commercial sector. In exemplary embodiments,the substrate 101 can be part of a car engine, such as a part of theinside of a piston. Although, the substrate 101 is not limited to theseexamples.

The coating on the substrate 101 can include a single emitting layer102. The emitting layer 102 can also include one or more layers. Theemitting layer 102 of the coating includes elemental isotopes with knownproperties that can be measured an analyzed by a spectroscopic method.The emitting layer 102 includes one or more of a stable isotope, a gammaray emitting isotope, an x-ray emitting isotope, a neutron scatteringisotope, neutron capturing isotope, or a combination thereof, which willbe described in further detail below. The isotopes provide a uniquesignature, or a distinguishing identification tag for the coating thatmay be observed by various atomic level measurement techniques, forexample, mass spectrometry, a gamma ray spectroscopy, scintillationdetection, or neutron spectroscopy.

The emitting layer 102 forms a base coating layer directly on thesubstrate 101 according to one or more embodiments. In otherembodiments, intermediate layers are formed between the substrate 101and the emitting layer 102 (not shown). The emitting layer 102 includesparticles that are micron-sized or nano-sized emitting particles. Theparticles may stand alone, being deposited directly onto the substrate101 to form the entire emitting layer 102, or may be mixed with a metalbinder to form a powder.

The emitting layer 102 can be formed by any desired method, whichdepends on the substrate 101, desired properties of the coating, and theparticular use of the substrate 101. Examples of methods for forming theemitting layer 102 include, but are not limited to, painting, powdercoating, primer methods, epoxy methods, RTV methods, thermal spraying,cold spraying, vapor deposition, liquid deposition, and electrolyticcoating methods.

The emitting layer 102 is thick enough or thin enough such that itcovers an entire surface (or in some cases limited to a criticalfeature/surface) of the substrate 101. The thickness of the emittinglayer 102 generally varies and is not intended to be limited. Thethickness of the emitting layer 102 is tailorable and depends on theamount of time that the emitting layer 102 is desired to be maintained.According to one or more embodiments, the emitting layer 102 is anatomic monolayer. The emitting layer 102 can be very thick, depending onthe application, and therefore, the thickness of the emitting layer 102is not intended to be limited. The emitting layer 102 does not have tobe a uniform thickness, and in some embodiments, the emitting layer 102has a non-uniform thickness.

As mentioned above, cold spraying is one method of forming the emittinglayer 102. Briefly, the cold spray process includes dispensing a powderof micron-sized or nano-sized emitting particles into a feeder of a coldspray machine. The particles can stand alone or be coated with a metalbinder to form a micron-sized powder. The particles are combined withpressurized gas and accelerated at a high velocity, such as about500-1500 m/s, and a low temperature, such as about 100 to 550° C., at asubstrate. The high velocity allows for plastic deformation to adherethe particles to the substrate, forming a coating of the emitting layer102.

FIG. 2 is a cross-sectional side view of an emitting layer 102 of acoating decaying according to embodiments. The emitting layer 102 emitsa signal 210 that is measured and detected by analytical spectroscopicmethods, depending on the composition of the emitting layer 102. Theemitting layer 102 includes stable isotopes, unstable isotopes, orblends of stable and/or unstable isotopes in some embodiments. In otherembodiments, the emitting layer 102 includes one or more unstableisotopes, such as a gamma ray emitting isotope, or a blend of gamma rayemitting isotopes. Yet, in other embodiments, the emitting layer 102includes one or more neutron capturing or scattering isotopes.

The signal 210 can be an isotopic signature that is detected by massspectrometry, for example. Unique isotopic signatures can be used as adistinguishing identification tag that indicates a property of thecoating such as where the coating was made (a source of the coating orthe manufacturer), when the coating was made, and/or what the coatingincludes, for example. The unique isotopic signature can also provide ameans of identifying information about the part, such as the serialnumber, model number, etc. The isotopic signature can be made unique andidentifiable by altering the ratio of stable and unstable isotopes.

The nucleus of each atom of an element includes protons and neutrons.The number of protons defines the element (e.g., hydrogen, carbon,etc.), and the sum of the protons and neutrons provides the atomic mass.The number of neutrons defines the isotope of that element. For example,most carbon (≈99%) has 6 protons and 6 neutrons and is written as ¹²C toreflect its atomic mass. However, about 1% of the carbon in the Earth'sbiosphere has 6 protons and 7 neutrons (¹³C), forming the heavy stableisotope of carbon. Stable isotopes of an element do not decay into otherelements. In contrast, radioactive isotopes (e.g., ¹⁴C) are unstableisotopes and will decay into other elements.

The less abundant stable isotope(s) of an element have one or twoadditional neutrons than protons, and thus are heavier than the morecommon stable isotope for those elements. Both heavy and light stableisotopes participate freely in chemical reactions and in biological andgeochemical processes. However, the rate at which heavy and light stableisotopes react during physical or chemical reactions differs. Thechemical bonds and attractive forces of atoms with heavy stable isotopesare stronger than those in the more common, lighter isotopes of anelement. As a result, the heavier isotopes react more slowly than thelighter isotopes, leading to isotopic separation or fractionationbetween reactant and product in both physical and biological reactions.Fractionation of the heavy and light stable isotopes is importantbecause it produces variation in the stable isotope ratio of differentelement pools and establishes an isotopic signal that can indicate theexistence or magnitude of key processes involved with elemental cycling.

The isotopic signature, and signal 210, including the relativefrequencies of stable and unstable isotopes, of an element can beartificially augmented in the emitting layer 102. The ratio of theisotopes can be determined by mass spectrometry, for example. Theisotopic signature of the emitting layer can be altered by introducing acombination of synthetic stable and unstable isotopic variations of anelement, such as, for example, americium, polonium, plutonium, carbon,or a combination thereof. Stable isotopes can be used in combinationwith unstable isotopes, as described below in FIG. 3.

To use the coating as a distinguishing identification tag for thearticle, spectroscopic analysis is performed on the coating. The signal(or spectral feature) received from the analysis is compared to a knownsignal (or spectral feature) of the coating that is known and determinedat the time of original formation of the coating on the article. Thecomparison provides unique identifying information about the coating andtherefore the article itself.

FIG. 3 is a cross-sectional side view of an emitting layer 102 of acoating emitting a gamma ray 310 according to embodiments. The gamma ray310 results from emission, or decay, of an unstable or metastableisotope of an element, with a characteristic fraction of events emittinggamma rays 310 of a specific energy. The unstable or metastable isotopeis an emissive tag for the coating.

The gamma ray 310 emitting isotopes may be relatively short-livedradioactive isotopes and may be added in just about any amount, providedthat they provide useful emission rates and safe handling. According toone or more embodiments, the gamma ray emitting isotope may be added ina range of parts per million to fractional parts per billion. Eachisotope may produce a characteristic energy (or energies) for thephotons emitted. It is this spectral character of the outputs thatallows identification of specific nuclear material that is in the item.The unique spectrum can be analyzed using, for example, a scintillationdetector or another radiation detector. Some non-limiting examples ofgamma ray 310 emitting isotopes include Barium-133, Calcium-109,Cobalt-57, Europium-152, Manganese-54, Sodium-22, Lead-210, and Zinc-65.

FIG. 4 is a cross-sectional side view of a layer 402 of a coatingaccording to embodiments. The layer 402 includes a neutron 410scattering and/or a neutron absorbing/capturing element. The neutron 410scattering or capturing element can be, but is not limited to, Boron¹⁰,Erbium, Gadolinium, Molybdenum, Titanium, Ytterbium, Cadmium,Dysprosium, Europium, Hafnium, Samarium, or Xenon.

When layer 402 is bombarded with neutrons 410, the layer 402 captures orscatters the neutrons. Analysis can be performed to determine the layerthickness of an attenuating layer having a known chemical composition.Understanding the part substrate material composition and thickness, theemitting layer composition and thickness, and then the composition ofthe attenuating layer will allow the calculation of the thickness of theattenuating layer. Such analysis could be performed, for example, with aMonte-Carlo simulation, such as Los Alamos National Lab's Monte CarloNeutral Particle analysis tool. When such an analysis is performed,backscattering is also considered. The radiated layer scatters into theactual part and then reflects back to the detector, and therefore, acombination of direct impingement, scatter, and backscatter are beingdetected. In order to accurately determine the thickness of the layer402, the material forming the part are known in fine detail, includingthe source layer, and substrate chemical composition and thickness.

FIG. 5 is a cross-sectional side view of a coating comprising anattenuating layer 503 arranged on an emitting layer 102 according toembodiments. One or more attenuating layers 503 are included in thecoating. The attenuating layer 503 protects the emitting layer 102 andthe substrate 101 from general wear and tear, and although not required,may be desirable. Even when an attenuating layer 503 is present on theemitting layer 102, emission from a radioactive element emitting asignal 510 in the emitting layer 102 can still be detected. According toone or more embodiments, the attenuations layer 503 is a pristineattenuating layer, with high attenuation.

The attenuating layer 503 can include one or more layers that are thesame or different. The composition of the attenuating layer 503 dependson the composition of the emitting layer 102. The attenuating layer 503can include a micron sized or nano sized metallic powder withattenuating characteristics, for example. The attenuating layer 503 canalso have gamma ray or neutron capturing properties. Other non-limitingexamples of materials for the attenuating layer 503 include Teflon,lacquers, plastics, paints, or a combination thereof.

FIG. 6 is a cross-sectional side view illustrating wear occurring in theattenuating layer 503 of a coating according to embodiments. Theattenuating layer 503 is a damaged/worn attenuating layer, with lowattenuation.

The crack 602 is shown to generally illustrate the wear and tear thatcan occur. As the attenuating layer 503 becomes worn, or cracked, astronger signal 510 from the emitting layer 102 will be detected. Thesignal indicates the degree of wear on the attenuating layer 503 and canserve as a warning that the device is in need of preventativemaintenance.

When the coating is used to determine a need for preventativemaintenance, a spectroscopic analysis is performed on a portion of thearticle comprising the coating. Spectroscopic methods allow enableisolation of signals from sources selected for the coating, which servesas a method rejecting noise from background radiation sources. Theresulting signal of all the primary and any secondary daughter productsis compared to the “as manufactured” data, and an assessment forattenuating layer thickness is possible. For example, a signal receivedfrom the spectroscopic analysis is compared to a known signal, such as acalibration curve. Based on the comparison, it is then determinedwhether the coating protecting the substrate has been worn and thereforewhether the article needs to be replaced or needs maintenance.

In embodiments in which an attenuating layer 503 is included in thecoating, a signal received from the spectroscopic analysis increases asthe attenuating layer wears and thins.

Any of the above embodiments described in FIGS. 1-6 can be employedindependently or in combination with one another to form the coatingdescribed herein. Furthermore, any of the embodiments of the coatingsdescribed in FIGS. 1-6 can be employed with the following methodsdescribed in FIGS. 7-9. For example, stable isotopes, unstable isotopes(e.g., gamma ray emitters), and/or neutron scattering/capturing elementscan be included in the coating.

FIG. 7 is a flow chart describing a method of identifyingcharacteristics of an article using a coating according to embodiments.In box 702, a substrate is provided. As described above, the substratecan include any one or more materials and can form a part of anyarticle. In box 704, a coating is formed on the substrate. Any of thecoatings described in FIGS. 1-6 can be employed independently or incombination. In box 706, the coated substrate 706 is put into amanufacturing supply chain, which can be used to manufacture a largerpart or device. Alternatively, the substrate itself may be entirelycoated with the coating to form a final article. In box 708, an atomiclevel property of the coating is measured and analyzed, for example, bya spectroscopic method. In box 710, characteristics of the substrate areidentified, such as the source of the substrate, the lot, themanufacturer, etc.

A method of identifying characteristics of an article using the coatingis described as follows according to an exemplary embodiment. On the dayof creation the coating will have a detectable spectral signal andbaseline intensity. The signal intensity for each radiating isotopedecreases exponentially with time, commonly referred to as thehalf-life. Various methods can be employed for forming the coating. Forexample, according to some embodiments, the coating can be doped with along-lived isotope with half-life, A, and a second dopant with a shorterhalf-life, B, which is scaled to the intended useful life of the productor coating. B should be much larger than A. In this fashion, B is acontrol for the decay of A, and A is indicative of layer age. However, Aalso should be long-lived, as well as deeply penetrating (high energy),so that it can freely pass through attenuating layers so that theattenuating layers do not affect the aging calculation. Subsequently,the high intensity B can be measured, and knowing its calibrationbaseline, the emitted versus calculated can then be compared. Thedifferences are attributed to the wear of the layer. One or both of thedopants are thus useful in determining wear of coating. Both are usefulin the identification of the product as an isotopic “fingerprint,” whichchanges through time when referenced to the baseline as-created state.As the number of emitting isotopes is increased, and initializedconcentration variation is controlled, this “fingerprint” is furtherstrengthened and becomes much more complicated to spoof.

FIG. 8 is a flow chart describing a method of determining a need forperforming preventative maintenance using a coating according toembodiments. In box 802, a substrate is provided. As described above,the substrate can include any one or more materials and can form a partof any device. In box 804, a coating is formed on the substrate. Any ofthe coatings described in FIGS. 1-6 can be employed independently or incombination. In box 806, the coated substrate is put into operation,alone or as part of a larger article. In box 808, an atomic levelproperty of the coating is measured and analyzed, for example, by aspectroscopic method. In box 810, the degree of wear on the substrate isdetermined.

FIG. 9 is a flow chart describing a method of passively aging a coatingaccording to embodiments. In box 902, a substrate is provided. Asdescribed above, the substrate can include any one or more materials andcan form a part of any article. In box 904, a coating is formed on thesubstrate. Any of the coatings described in FIGS. 1-6 can be employedindependently or in combination. In box 906, the coated substrate is putinto operation, alone or as part of a larger article. In box 908, theage of the coating is determined.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiments were chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

While the preferred embodiments to the invention have been described, itwill be understood that those skilled in the art, both now and in thefuture, may make various improvements and enhancements which fall withinthe scope of the claims which follow. These claims should be construedto maintain the proper protection for the invention first described.

What is claimed is:
 1. A method of forming a coating on an article, themethod comprising: forming a coating comprising an emitting layer, theemitting layer comprising an elemental isotope with a known propertythat can be measured by a spectroscopic method, the elemental isotopeproviding a distinguishing identification tag for the coating, and thecoating providing a layer of protection to the substrate; and depositingthe coating on a surface of a substrate of the article; wherein theelemental isotope is a stable isotope, an unstable isotope, a neutronscattering isotope, a neutron capturing isotope, or combinationsthereof.
 2. The method of claim 1, wherein the coating is deposited by acold spraying method.
 3. The method of claim 1, wherein the coating isdeposited by painting, powder coating, primer method, epoxy method, RTVmethod, thermal spraying, vapor deposition, liquid deposition,electrolytic coating, or a combination thereof.
 4. The method of claim1, wherein the coating further includes an attenuating layer disposed onthe emitting layer that protects the emitting layer.
 5. The method ofclaim 1, wherein the elemental isotope is an unstable isotope.
 6. Themethod of claim 5, wherein the unstable isotope is a gamma ray emittingisotope.
 7. The method of claim 1, wherein the coating comprisesmicron-sized particles or nano-sized particles comprising the elementalisotope.
 8. The method of claim 1, wherein the elemental isotope is ablend of stable and unstable isotopes of an element that differs from anatural abundance.
 9. The method of claim 1, wherein the spectroscopicmethod is mass spectrometry, radiation detection, or a combinationthereof.
 10. The method of claim 1, wherein the distinguishingidentification tag indicates where the coating was made, when thecoating was made, what the coating comprises, provides identifyinginformation, or a combination thereof.
 11. A method of determining aneed for preventative maintenance on an article, the method comprising:performing a spectroscopic analysis on a portion of the articlecomprising a coating, the coating comprising an emitting layer, theemitting layer comprising an elemental isotope that can be measured bythe spectroscopic analysis, and the coating providing a layer ofprotection to the substrate; comparing a signal received from thespectroscopic analysis to a calibration curve; and determining, based ona comparison, whether the coating protecting the substrate has been wornand therefore whether the article needs maintenance; wherein theelemental isotope is a stable isotope, an unstable isotope, a neutronscattering isotope, a neutron capturing isotope, or combinationsthereof.
 12. The method of claim 11, wherein the elemental isotope is anemissive tag.
 13. The method of claim 12, wherein the emissive tag is agamma ray emitting isotope.
 14. The method of claim 13, wherein thecoating comprises micron-sized particles or nano-sized particlescomprising the elemental isotope.
 15. The method of claim 11, whereinthe coating further comprises an attenuating layer arranged on theemitting layer.
 16. The method of claim 15, wherein the attenuatinglayer protects the emitting layer, and the signal received from thespectroscopic analysis increases as the attenuating layer wears andexposes the emitting layer.
 17. A coating of an article, comprising: anemitting layer arranged on a substrate of the article, the emittinglayer comprising an elemental isotope with a known property that can bemeasured by a spectroscopic method, the elemental isotope providing adistinguishing identification tag for the coating, and the coatingproviding a layer of protection to the substrate; and an attenuatinglayer arranged on the emitting layer, the attenuating layer protectingthe emitting layer; wherein the elemental isotope is a stable isotope,an unstable isotope, a neutron scattering isotope, a neutron capturingisotope, or combinations thereof.
 18. The coating of claim 17, whereinthe emitting layer comprises micon sized or nano sized emittingparticles.
 19. The coating of claim 18, wherein the attenuating layercomprises micron sized or nano sized particles.
 20. The coating of claim17, wherein the emitting layer comprises gamma ray emitting particles orx-ray emitting particles.